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Earth formed around 4.54 billion years ago [2] [3] [4] by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere, which contained almost no oxygen and would have been toxic to humans and most modern life. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme ...
On a prograde planet like the Earth, the sidereal day is shorter than the solar day. At time 1, the Sun and a certain distant star are both overhead. At time 2, the planet has rotated 360° and the distant star is overhead again (1→2 = one sidereal day). But it is not until a little later, at time 3, that the Sun is overhead again (1→3 = one solar day). More simply, 1→2 is a complete ...
The Earth's axial tilt changes slowly over thousands of years but its current value of about ε = 23.44° is nearly constant, so the change in solar declination during one year is nearly the same as during the next year. At the solstices, the angle between the rays of the Sun and the plane of the Earth's equator reaches its maximum value of 23.44
All the solar planets more distant from the Sun than Earth are similar to Earth in that, since they experience many rotations per revolution around the Sun, there is only a small difference between the length of the sidereal day and that of the solar day – the ratio of the former to the latter never being less than Earth's ratio of 0.997.
As at Jan 3, 2025, solar cycle 25 is averaging 39% more spots per day than solar cycle 24 at the same point in the cycle (Jan 3, 2014). Year 1 of SC25 (Dec 2019 to Nov 2020) averaged 101% more spots per day than year 1 of SC24. Year 2 of SC25 (Dec 2020 to Nov 2021) averaged 7% more spots per day than year 2 of SC24.
The sidereal year differs from the solar year, "the period of time required for the ecliptic longitude of the Sun to increase 360 degrees", [2] due to the precession of the equinoxes. The sidereal year is 20 min 24.5 s longer than the mean tropical year at J2000.0 (365.242 190 402 ephemeris days) .
The Maunder Minimum occurred within the Little Ice Age, a long period (c. 1300 – c. 1850) of lower-than-average European temperatures. [9] The reduced solar activity may have contributed to the climatic cooling, although the cooling began before the solar minimum and its primary cause is believed to be volcanic activity. [10]
Solar luminosity was 30% dimmer when the Earth formed 4.5 billion years ago, [14] and it is expected to increase in luminosity approximately 10% per billion years in the future. [15] On very long time scales, the evolution of the sun is also an important factor in determining Earth's climate. According to standard solar theories, the sun will ...